linux-kernel - Re: [RFC] sched: check RT runqueue overloaded in tick timer

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Message-ID: <BANLkTi=xw04C7k7g9k7uaeGBmsz9h+Vydw@mail.gmail.com>
Date:	Thu, 30 Jun 2011 21:13:12 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] sched: check RT runqueue overloaded in tick timer

On Thu, Jun 30, 2011 at 8:55 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Thu, 2011-06-30 at 20:47 +0800, Hillf Danton wrote:
>> Hi Steven
>>
>> When tick timer runs, runqueue overload is checked. If overloaded and other
>> CPUs available at the moment, reschedule is fired to allow push logic to move
>> the pushable tasks somewhere else.
>
> Why?
>
> This would be a waste of overhead. We check when a task is queued and
> dequeue, and when a cpu lowers its priority (for a pull). There's no
> need to randomly check if we need to push or pull based on timers.
> That's just going to slow things down.
>
Got it.

If puller is inactive, there is no CPU available for the pushable.

Thanks
Hillf
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